"It costs less than to lose your crop," the weather expert replied. "Usually you can figure that a frosty night will take a gallon of oil per tree, or from twenty to twenty-five cents. In a fruit growing section a grower is unlikely to have more than four or five still, freezing nights a year when his crop may be ruined by frost, so that he will spend a dollar or so per tree in protecting his orchard. As there are few fruit trees which bring in a profit of less than ten dollars during the season, and some a great deal more--according to the nature of the crop--the proportionate expense of heating is small compared with the amount of fruit saved." "Then you think that heating an orchard will save the fruit?" "Absolutely without any question," the weather expert answered. "And, if the fruit-grower will keep in close touch with the Weather Bureau, he will know when precautions are necessary. Of course, boys, it's especially important for this work that there are a number of co-operative observers, because frost is not a widespread general phenomenon. You could have a fearful killing frost down in the hollow where Anton's house is, or in the low ground near your house, Ross, and still Tom's place, on that little hill, would be quite safe. One of the things that the League of the Weather ought to be able to do this winter and spring is to see that frost is fought. Even when your fathers haven't got regular oil-pots, boys, a few smudges with heavy smoke, drifting over the orchards or the truck fields, if started early enough in the evening may check a freeze." "Why, sir?" asked Ross. "Smoke isn't hot." "No, my boy. But you remember that I told you that the cold was caused by the radiation of heat from the earth escaping into the air and through it. If there's a steady layer of smoke, like a blanket, floating across the land, the heat radiating from the earth will not have a chance to escape to the upper air. It will stay in the lower layer of the air and thus keep it from dropping to the killing temperatures of a true freeze. That's what the Indians of the pueblos used to do." In the mild winters and early springs of Issaquena County, there seemed little reason for the boys of the League to trouble themselves with frost warnings, but, at the Forecaster's urgency, the boys kept wide awake for it. It happened, though, that the lads had talked so much about their frost protection plans that several of the farmers decided to get some oil-burning fire-pots for use that spring, in the event of a freeze. Jed Tighe, however, one of the few people of the neighborhood who had shown but a perfunctory interest in the League, laughed to scorn the idea of buying the fire-pots, as Fred had suggested in a recent issue of the _Review_. Even Jed Tighe read the little sheet every week, in spite of his alleged scornfulness.